UR1213 Herbivores, INRA Clermont-Ferrand/Theix, 63122 Saint-Genès-Champanelle, France.
Animal. 2012 Mar;6(3):518-25. doi: 10.1017/S175173111100156X.
The release rate (RR) of sulphur hexafluoride (SF(6)) gas from permeation tube in the rumen appears to be positively related with methane (CH(4)) emissions calculated using the SF(6) tracer technique. Gas samples of breath and ruminal headspace were collected simultaneously in order to evaluate the hypothesis that transactions of SF(6) in the rumen are the source for this relationship. Six non-lactating dairy cows fitted with rumen cannulae were subdivided into two groups and randomly assigned to a two-period crossover design to permeation tubes with low RR (LRR = 1.577 mg/day) or two-times higher RR (HRR = 3.147 mg/day) RR. The cows were fed limited amounts of maize silage (80% ad libitum) split into two meals (40% at 0800 h and 60% at 1600 h). Each period consisted of 3-day gas sampling. Immediately before the morning feed and then each hour over 8 h, ruminal gas samples (50 ml) were withdrawn through the cannula fitted with stoppers to prevent opening. Simultaneously, 8-h integrated breath gas samples were collected over the same period. Ratios of concentration of CH(4)/SF(6), CO(2)/SF(6) and CO(2)/CH(4) and emission estimates of CH(4) and CO(2) were calculated for each sample source using the SF(6) tracer technique principles. The LRR treatment yielded higher (P < 0.001) ruminal CH(4)/SF(6) (by 1.79 times) and CO(2)/SF(6) (by 1.90 times) ratios than the HRR treatment; however, these differences were lower than the 2.0 times difference expected from the RR between the LRR and HRR. Consequently, the LRR treatment was associated with lower (P < 0.01) ruminal emissions of CH(4) over the 8-h collection period than with the HRR treatment (+11%), a difference also confirmed by the breath samples (+11%). RR treatments did not differ (P = 0.53) in ruminal or breath CO(2) emissions; however, our results confirm that the SF(6) tracer seems inappropriate for CO(2) emissions estimation in ruminants. Irrespective of the RR treatment, breath samples yielded 8% to 9% higher CH(4) emission estimates than the ruminal samples (P = 0.01). The relationship between rumen and breath sources for CH(4) emissions was better for LRR than for HRR treatment, suggesting that tracer performance decreases with the highest RR of SF(6) tested in our study (3.1 mg/day). A hypothesis is discussed with regard to the mechanism responsible for the relationship between RR and CH(4) emission estimates. The use of permeation tubes with small range in RR is recommended in animal experiments to decrease variability in CH(4) emission estimates using the SF(6) tracer technique.
六氟化硫（SF6）气体从渗透管中的释放率（RR）似乎与使用 SF6 示踪技术计算的甲烷（CH4）排放量呈正相关。为了验证 SF6 在瘤胃中的代谢是这种关系的来源这一假设，同时采集了呼吸和瘤胃顶空的气体样本。将 6 头安装有瘤胃套管的非泌乳奶牛分为两组，并随机分配到两期交叉设计中，分别使用 RR 较低（LRR = 1.577mg/天）或 RR 较高（HRR = 3.147mg/天）的渗透管。奶牛被喂食限量的玉米青贮（80%自由采食），分为两餐（40%在 0800h，60%在 1600h）。每个时期都包括 3 天的气体采样。在早上喂食前和 8 小时内的每小时，通过安装有塞子的套管抽取 50ml 的瘤胃气体样本，以防止打开。同时，在同一时期采集 8 小时的综合呼吸气体样本。使用 SF6 示踪技术原理，为每个样本源计算 CH4/SF6、CO2/SF6 和 CO2/CH4 的浓度比以及 CH4 和 CO2 的排放估计值。LRR 处理产生的瘤胃 CH4/SF6（高 1.79 倍）和 CO2/SF6（高 1.90 倍）比值高于 HRR 处理；然而，这些差异低于 LRR 和 HRR 之间 RR 差异的 2.0 倍。因此，与 HRR 处理相比，LRR 处理在 8 小时采集期间与 HRR 处理相比，瘤胃 CH4 的排放量较低（P < 0.01），呼吸样本也证实了这一点（低 11%）。RR 处理在瘤胃或呼吸 CO2 排放方面没有差异（P = 0.53）；然而，我们的结果证实，SF6 示踪剂似乎不适合估算反刍动物的 CO2 排放。无论 RR 处理如何，呼吸样本的 CH4 排放估计值都比瘤胃样本高 8%至 9%（P = 0.01）。LRR 处理比 HRR 处理更能反映瘤胃和呼吸源之间的 CH4 排放关系，这表明示踪剂性能随着我们研究中测试的最高 RR（3.1mg/天）而降低。讨论了一种关于 RR 与 CH4 排放估计值之间关系的机制的假设。建议在动物实验中使用 RR 范围较小的渗透管，以减少使用 SF6 示踪技术时 CH4 排放估计值的变异性。
